Deciding on Frame Size

[Krank]

Hi.

I am trying to choose which frame size of the 2013 Bianchi Infinito (61cm vs 59cm) and ask for your help....

I am not wanting to go down the Sempre Pro route.
I have also reviewed numerous bike-fit sites....
I want to ride distances of 100km and beyond in an aggressive low profile riding position.

My body dims:
- Height 188.6cm
- In-seam 87cm
- Torso length 69cm
- Arm reach 70cm
- Total reach or top tube + stem ([(Torso Length + Arm Length) / 2] + 4") 79.6cm

The following differences in bike dimensions between these frames exist:

59cm frame
effective top tube - 57.5cm
effective seat tube length - 59cm
head tube length - 205cm
front centre - 607cm

61 frame
effective top tube - 58.5cm
effective seat tube length - 61cm
head tube length - 225cm
front centre - 612cm

Your thoughts on which frame size to suit my application??

Krank

[TDC]

I would assume the smaller frame will allow a more aggressive position. 2 cm shorter head tube should allow a greater saddle - handlebar drop.

[greyhoundtom]

I'm 188.5 cm and went for a 61 cm frame with a 58.5 cm top tube when I bought mine, and the end result was having to fit a 90 mm stem to make the bike fit comfortable.

I really wish I had gone for a 59 cm frame instead of the 61 cm.

It’s much easier to make a frame that is slightly too small fit comfortably, than a frame that is a fraction too large.

[Krank]

Thanks very much guys.

greyhoundtom -
- How do your other body dims noted in OP compare to mine?
- What is the impact of going to a smaller head stem at 90cm?
- How do you find the longer head tube in long rides?
- What stem would you have fitted if you had the 59cm frameset?

TDC -
- How would the shorter Front Center dimension on the 59cm benefit (if at all)?



Krank

[TDC]

probably quicker handling and more responsive turn in to the corners. Chain stays are the same length,and the HTA on both is 72.5 (and I would assume the fork trail is the same on both), according to the geo charts, so wheel base is slightly shorter with weight distribution pushed slightly to the front because of the front centre dimension.

[greyhoundtom]

Thanks very much guys.

greyhoundtom -
- How do your other body dims noted in OP compare to mine?
Very similar......within a few mm
- What is the impact of going to a smaller head stem at 90cm?
Not a great impact other than making the steering a fraction twitchy
- How do you find the longer head tube in long rides?
The longer head tube increases reach therefore unless your core strength is real good, (and mine is not) the end result is more weight on your hands which for me causes numbness.
- What stem would you have fitted if you had the 59cm frameset?
Others may have a different opinion, but I believe the minimum stem length for comfortable steering is 100 mm, and that is what I would have had if I had the 59 cm frame

TDC -
- How would the shorter Front Center dimension on the 59cm benefit (if at all)?



Krank

[Krank]

Thanks guys.

This is excellent information!

Greyhoundtom - are you able to change anything else to make your bike optimal for your fit?


krank

[TDC]

I just did some rough calculations of stack and reach for the 2 sizes, and because of the slacker seat angle (72.5 on the 61 vs 73 on the 59) on the 61, the reach is pretty much the same on both frames

[Krank]

Thanks TDC.

I guess I now need some clarification on reach between these 2 framesets.

Greyhoundtom states the increased HT increases reach. You have stated the reach is the approx. same due to slightly different seat angles....

Also - What is an optimal saddle - handlebar height for low profile aggressive riding to take advantage of the lower HT on the 59cm frameset?

Krank

[NeillS]

I'm a fledgling bike fitter and sports physio by trade. My thoughts and questions for you;

How flexible is your lumbar and thoracic spine?
How do you quantify such a thing?
Are you a strong, mild or neutral heel dropped under load? Or the more rare toe dropper? This will affect seat height drastically and as such, bar drop and whatnot.
Are your legs "functionally long" on the bike? That is, do you have any idea when your seat height is too high? Measuring angles on a computer doesn't count here unfortunately. If your neural or mechanical length of hamstrings prohibits you from tilting your pelvis anteriorly on the seat, it will cause a shorter effective torso length and vice versa.

I'm not trying to be an ass about it, but the simple fact is - the way you interact with the bike can NOT be determined in any meaningful way by measuring yourself with a tape. Vast differences exist in terms of functional reach depending in large part on how your pelvis sits, how easily it rotates forwards and how well your spine flexes.

Your best bet is, quite simply, to go and sit on each one, pedal on a trainer for a while and see how you feel. An even better idea is to get a quality bike fitter to assess you on your current bike and then match the geometry to whichever frame suits best. For an expensive bike that may last you for five years, this is a good idea!

[TDC]

Thanks TDC.

I guess I now need some clarification on reach between these 2 framesets.

Greyhoundtom states the increased HT increases reach. You have stated the reach is the approx. same due to slightly different seat angles....

Also - What is an optimal saddle - handlebar height for low profile aggressive riding to take advantage of the lower HT on the 59cm frameset?

Krank

Reach is the amount of top tube in front of the BB. Maybe Tom and I are describing different things. You have probably seen this stuff, but the Cervelo site has a good description of stack and reach. Given that we generally position our saddles relative to the BB, this wont change on either the 59 or 61. You would have you seat further forward by some amount on the 61 to achieve the same relationship to the BB (you dimension are constant in all this) as the extra cm of TT is accounted for behind the BB in the frame set back, which is the proportion of the TT behind the BB.

http://www.cervelo.com/en/engineering/t ... d-fit.html

Anyway, I think Neill has the right idea, first you should establish if you are designed to ride a low, aero, and aggresive set up.

[Krank]

Thanks Neil.

Unfortunately, no Bianchi dealer in Australia will stock the 2013 Infinito.

They will only supply the frameset after you order it, so it is impossible "to go and sit on each one".

I ride 550km per month and so I do not have a need to "pedal on a trainer for a while and see how i feel". I have core strength, I stretch well and I am flexible.

I do understand what you are saying and your ideals are fine in an ideal world.

TDC - Thanks for the link! I currently ride the 2007 928 bianchi in the low aggressive, aero setup with a 60mm height gap between the saddle and handlebars, 155mm Head Tube without any spacers and a 100mm Head Stem. Been doing this now for 2 years.



Krank

[cpical]

Get one of each!

[TDC]

ok. I just looked up a geo chart of a 928. 155 mm head tube is on the 55 cm. TT is 555mm. The 59 will be a much more relaxed position than what you have now.

[Krank]

ok - thanks TDC.

Can you give me the link showing the 928 dims of this HT? I cannot locate it.

My 57cm frame measures to the published 57cm frame with the other members. Perhaps the 55cm and 57cm frame share the same HT for the 928?

I feel that my current 57 frame is too small for me.

krank

[Krank]

Get one of each!

Yes - indeed! Perhaps the Oltre instead??

[TDC]

http://www.bianchiusa.com/archives/2007 ... e-compact/

[Krank]

thanks TDC.

Sorry - This is the bike I have - 2006 928 RC - 57cm.

http://www.bianchiusa.com/archives/2006 ... gedchorus/

are you able to calculate stack and reach on both my current 2006 RC 928 and my proposed 59cm 2013 Infinito?

it would be interesting to observe the differences...


Krank

[TDC]

From what i can work out,

Stack Reach Frame set back
59 564 402.5 172.5
61 581.7 401.6 183.4
57 (928) 546 398 162

[Krank]

Thanks TDC.

Based on these values, how do you think the 59cm Infinito will handle with my body dims compared to my current 928 RC - all other things being equal??


Krank

[TDC]

Probably (generally speaking) feel a bit slower or less nimble.

[Krank]

mmm perhaps I may look at the 57cm frame on the infintio?

or just keep my existing bike??

but, i am real keen on having EPS and SR 11 speed gruppo.

My existing bike just feels too small.

Krank

[greyhoundtom]

You are currently riding a 57 cm framed bike and yes that would feel too small for someone with your body dimensions.

Because you are used to riding a relatively small frame going to a 59 cm frame will make a difference, and it certainly will feel larger, more comfortable, and slightly less aggressive due to the reduction in the top of saddle to top of handle bar dimension.

Going to a 61 cm frame would IMHO be too big a jump in size, and may actually feel a bit too large considering you are used to a 57 cm frame.

In your shoes my choice would be the 59 cm frame.

[Krank]

Thanks Greyhoundtom.

Yes, I know my back is not angled correctly when I am on the current bike and my arms splay out too much.

Do you actually own the 2012 infinito or another bike in the 61cm frameset?

Krank

[greyhoundtom]

No mate my bike is an old model Fuji, a 61 cm 2007 Team that I have since upgraded with an Ultegra groupset, CF handle bars, and a CF seat post.

However the geometry is very similar in regard to seat tube angle and effective top tube length.